DE19542808A1 - Vitreous coating of substrate by spraying - Google Patents

Abstract

Coating of a substrate with a vitreous material layer(4,6,8,10) is carried out by spraying. Also claimed is a high temp. fuel cell stack comprising various planar components which are gas-tightly joined together by and mutually electrically insulated by a vitreous material layer produced by spraying. Pref. the substrate (2) is preheated at up to 600 deg C and the layer surface (12) is smoothed by a plasma or high velocity flame after spraying.

Description

The invention relates to a method for coating a substrate with a layer of a glass-like sub punch.

With various components, for example the planar Components of a high-temperature fuel cell stack, it is necessary, for example for an electrical or gastight insulation of the components against each other, substrates to be coated with a glassy substance.

The planar components are usually connected with glass solders or with composite glass solders. A suitable one Composite glass solder exists e.g. B. from a glass base of B₂O₃- SiO₂-CaO and corresponding ceramic composite parts from z. B. ZrO₂ and MgO. The advantage of glass solders is, among other things in the possibility, both in atmosphere and in vacuum to be able to solder.

In particular from the "Fuel Cell Handbook" by A. J. Appelby and F. R. Foulkes, pages 443 to 454, it is known that at a high-temperature fuel cell stack, in the specialist elite a fuel cell stack is also called a "stack", different planar components stacked on top of each other the. The rei lie under an upper planar cover plate order of a contact layer, a solid electrolyte elec troden element, another contact layer, another bi polar plate etc. on top of each other. Each form a two between two adjacent bipolar plates trolytic electrode element, including the one on both sides Solid electrolyte electrode element directly adjacent Contact layer and the adjacent to the contact layer Side of each of the two bipolar plates, together one High temperature fuel cell.  

A practiced technique to put the different together planar components are made with so-called green foils. At such green foils, the composite glass solder together with egg mixed organic binder system and z. B. using tape Casted to a film about 200 to 400 microns thick. Of the Binder content in this system is usually approx. 20 % By weight. These green foils can then be cut with a knife structured and on the desired surface of a planar Component are applied.

The density of the glass solder in such foils is due to the high volume fraction of the binder system is relatively low. After assembling the components and burning out the Binder shrinks the green sheet up to Can be 80%. Because between the individual planar components ment gas-bearing ducts and rooms are formed must be separated from each other in a gastight manner gastight separation of the different channels and rooms due to the shrinkage when using green foils only difficult to achieve and with great uncertainty.

Furthermore, the organic binder system must be free of residues be removed from the green sheet. Between the different Planar components can cause additional problems lead because the released substances, such as. B. Binder, Dispersants, solvents and plasticizers, only very much bad about when assembling the planar devices resulting seals can escape to the outside. Inside Ren of the fuel cell stack is therefore a residue free burning of these released substances not ge ensures.

The disadvantages mentioned lead to a reduction in lei density or even inoperability of the High temperature fuel cell stack.

The invention is based on the object of a method specify for coating a substrate in which the before mentioned disadvantages can be avoided. Also lies the invention has the object of a high-temperature firing to specify the cell stack at which the power density of the high-temperature fuel cell stack by joining gene of the high-temperature fuel cell stack planar components is not reduced.

The first object is achieved according to the invention with the features of claim 1. The second mentioned Gabe is solved according to the invention with the features of Claim 8.

In the method for coating a substrate with a Layer of a glassy substance is according to the Erfin the glassy substance by spraying onto the substrate applied. In this process there are no binding agents needed, d. H. that the coating once created on the Substrate maintains its consistency and composition. It there are also no substances that are released unwanted side effects. The procedure can different environmental conditions are carried out at for example at atmospheric pressure or in a vacuum. Thereby flexible application is guaranteed.

Glass, glass solder, compo are among glassy substances to understand sit glass solder or a glass ceramic. This much number of glassy substances to be used a coating optimized for the respective application tung.

Preferably, when coating with a glass-like Substance that contains at least two components, the compo agglomerated and sprayed together. Depending on the setting of the glassy substance, for example from a Glass ceramic, the individual components before the fuel  prepared and sprayed together or separately for spraying be sprayed together after preparation. So regardless of the composition of the glass ceramic a uniform procedure for the preparation Depending on whether there is sufficient electrical conductivity or a possible seal against gaseous Komo components, the components of the Glass ceramics selected and compiled accordingly and applied to the substrate.

In a further embodiment according to the invention, the Surface of the layer after spraying through a plasma or High-speed flame smoothed. This will make the The quality of the layer is also improved.

In particular, several layers are applied one above the other gene, which is composed of glass-like substances Zen.

In a further embodiment according to the invention, between two successive layers of glassy Substance a layer of a non-vitreous substance, in particular a ceramic applied.

In particular, the substrate is coated up to Heated to 600 ° C.

The method is preferably according to one of the preceding Claims for the production of a high temperature distillery used cell stack. Performance losses, conditional through a burnout of organic binder, which is often caused by the assembly of the planar components, the one Form high-temperature fuel cell stacks, who emerge largely avoided.

In the high temperature fuel cell stack that various whose planar components comprise, are the individual planar  Components according to the invention by a layer of a glassy substance gas-tight interconnected and elec trically isolated from each other, the layer by fuel zen is generated. With a high temperature fuel cell a large number of planar components must be stacked together who are connected. As a result, there is also a large number number of layers of vitreous substance that the individual NEN planar components connect so that a Improvement regarding these connections is crucial on increasing the overall performance of the entire high temperature raturation fuel cell stack affects.

To further explain the invention, the Ausfü Example of the drawing referenced. Show it:

Fig. 1 and Fig. 2 respectively according to the invention a coated substrate.

Fig. 3 shows a section according to the invention from egg nem high temperature fuel cell stack.

Referring to FIG. 1, a layer 4 is coated from a glassy substance tightly on a substrate 2. This layer 4 is produced by spraying. Glass, glass solder, composite glass solder or a glass ceramic can be used as the glass-like substance. In this case, easy-melting soldering glasses are referred to as glass solder, which are characterized by low viscosity and small surface tensions and whose fusion temperature is between 400 and 700 ° C. Glass ceramics, on the other hand, are a designation for polycrystalline solids that are produced by a ceramization, ie a controlled devitrification of glasses. These glasar term substances can be applied in a very dense and adherent manner to the substrate 2 in the powdery state.

When using a glass ceramic, the various powdery components of the glass ceramic suitable for the respective case can be separated or agglomerated together in a fluidized bed and then sprayed onto the substrate 2 together. All common materials such as. B. AL₂O₃, Y₂O₃, CeO₂, spinels, MgO, Al₂TiO₅, TiO₂, CoO, SnO₂ in question. The grain sizes of the Kerami ken can vary between 1 µm and 50 µm.

The atmospheric Plasma spraying, high speed flame spraying or vacuum plasma spraying can be used.

In order to smooth the surface 12 of the sprayed-on layer 4, there is the possibility of subsequently treating the surface 12 of the layer 4 with a plasma flame or a high-speed flame using a short-time melting process. In addition, the properties of layer 4 can be further improved by repeated spraying and short-time melting.

The quality of layer 4 depends on the setting of the spraying devices and spraying parameters. When plasma zen z. B. the spraying distance is usually between 60 and 120 mm, while the substrate 2 can be heated up to 600 ° C in a previous process. Furthermore, the quality of the adherent layer 4 is additionally influenced by the powder delivery rate of the spraying process.

The quality of the surface smoothing of the surface 12 of the layer 4 depends on the duration of the aftertreatment.

In a further step, additional layers 6 , 8 and 10 made of glass-like substance can be applied to the first applied layer 4 in further spraying processes. The individual layers 4 , 6 , 8 , 10 can have different compositions, so that the properties of the layers 4 , 6 , 8 , 10 can also vary. With such a layer sequence 4 , 6 , 8 , 10 arranged individually, almost any desired material property can be realized.

As a substrate 2 , on which the layers 4 , 6 , 8 , 10 are applied, ceramics or metals can be used. Suitable ceramics are, for example, ZrO₂, Al₂O₃, spinels, perovskites and lanthanum chromium oxides. As a metal z. B. CrFe5Y₂O₃1, HA230, stainless steels and various industrial steels suitable.

Accordingly, Fig. 2 is applied to a substrate 14 is first ramikschutzschicht a Ke 16th On the ceramic protective layer 16 , in turn, a layer 18 of a glass-like substance is applied. This is followed by a ceramic protective layer 20 and then another layer 22 made of a glass-like substance. The ceramic protective layers 16 and 20 are preferably made of ZrO₂, Al₂O₃ or spinels. As Spi nelle preferably MgAl₂O₄ or MgO · MgAl₂O₄ come into question. The order in which the layers 16 , 18 , 20 , 22 are applied to the substrate 14 can be changed as required depending on the requirement. Accordingly, not only layers 18 , 22 of vitreous substance can be applied in succession, but the layer sequence can also include layers 16 , 20 that do not consist of vitreous substance.

Referring to FIG. 3, a high temperature fuel cell stack 30 comprises a high-temperature fuel cell installation at least two planar components 32 and 34 which are connected by a strongly adhering layer 36 of a glassy substance. The planar components 32 and 34 can, for. B. as a bipolar plate, as a window film or as a solid electrolyte electro denelement.

Composite glass solders are particularly suitable as glass-like substance for this purpose, for example 75% by weight from a glass solder, e.g. B. B₂O₃-SiO₂-CaO and / or BaO, and 25 wt .-% of a ceramic such as. B. ZrO₂, MgO or Al₂O₃, exist as a mixture. Individual components of the ceramic portion are present in a very fine-grained form as nucleating agents. The metallic components of the planar components 32 , 34 be in the high-temperature fuel cell stack 30 z. B. from CrFe5Y₂O₃1.

The described in connection with FIGS. 1 and 2 Ver drive for coating a substrate 2 , 14 is thus very well suited for the connection of the planar components 32 and 34 of a high-temperature fuel cell stack 30 of a high-temperature fuel cell system.

Claims (8)

1. A method for coating a substrate ( 2 , 14 ) with a layer ( 4 , 6 , 8 , 10 , 18 , 22 ) of a glass-like substance, in which the glass-like substance is sprayed onto the substrate ( 2 , 14 ) is applied. 2. The method according to claim 1, in which when coating with a glassy substance that has at least two components contains, the components agglomerated and ge together be injected. 3. The method according to any one of the preceding claims, wherein the surface ( 12 ) of the layer ( 4 , 6 , 8 , 10 , 18 , 22 ) after the spraying is smoothed by a plasma or high-speed flame. 4. The method according to any one of the preceding claims, in which a plurality of layers ( 4 , 6 , 8 , 10 , 18 , 22 ) are applied one above the other, each of which is composed of glass-like substances. 5. The method according to claim 4, wherein a layer ( 20 ) of a non-vitreous substance, in particular a ceramic, is applied between two successive layers ( 18 , 22 ) of a vitreous substance. 6. The method according to any one of the preceding claims, wherein the substrate ( 2 , 14 ) is heated to up to 600 ° C before coating. 7. Use of the method according to one of the preceding claims for the production of a high-temperature fuel cell stack ( 30 ). 8. High-temperature fuel cell stack, which comprises various planar components ( 32 , 34 ), in which the individual planar components ( 32 , 34 ) are gas-tightly connected to one another and electrically insulated from one another by a layer ( 36 ) of a glass-like substance, the Layer ( 36 ) is generated by spraying.